How to grow Cosmos
Updated October 2026
Cosmos is an easy, fast growing summer annual from Mexico with airy, lacy foliage and daisy-like flowers that feed bees, butterflies and other beneficial insects. It flowers from summer until frost with very little care, prefers lean soil to rich, and reseeds readily. It is a natural partner for the vegetable garden, where its flowers draw pollinators and predators.
📖 Our full guide: How to Grow Cosmos
Where to plant
Grow cosmos where it gets at least half a day of direct sun, in loose, well drained soil. It flowers best in lean ground; rich soil and heavy feeding give tall, floppy plants with fewer flowers. Tall types may need staking in windy, stormy spots.
Sow after the last frost once the soil has warmed to at least 65°F. In Florida, the Gulf South, Texas and the desert, sow in spring and again in late summer, and South Florida can sow from late summer through winter. In California, sow from March to July. Across the North, the Midwest, the Mountain West, the Pacific Northwest and Alaska, sow in late May or June.
Choosing a variety
Garden cosmos (Cosmos bipinnatus) has pink, white, lavender and maroon flowers on plants up to 4 or 5 feet tall. Sensation is a tall classic, Sonata and Antiquity are compact and early, and Seashells has rolled, tube shaped petals. Klondike cosmos (Cosmos sulphureus), including the Cosmic series, has yellow, orange and red flowers and handles heat well; compact Cosmic types reach 12 to 18 inches.
How to plant
- Wait until after the last frost, when the soil is at least 65°F.
- Rake the seed lightly into loose soil; sowing too deep hinders germination.
- Keep the soil moist for the first 5 to 10 days. Seedlings appear in 7 to 21 days.
- Thin to about 12 inches (30 cm) apart, closer for compact varieties.
- Sow again a few weeks later, or in late summer in the South, for a longer show.
Watering and feeding
Water seedlings until established, then sparingly. Cosmos tolerates dry, porous soils and dislikes being kept wet.
Do not fertilize. Rich soil and extra nitrogen give leafy, floppy plants and fewer flowers.
Pruning and care through the year
- Deadhead to keep the flowers coming.
- When spring sown Klondike cosmos is covered in dry seed, NC State suggests cutting the plants back to 12 to 18 inches; they rebloom in about a month and the dropped seed adds new plants.
- Stake tall varieties or grow them among sturdier plants.
- Cosmos reseeds readily; pull unwanted seedlings in spring.
Cutting flowers
Cut stems when the flowers are just opening; regular cutting encourages more blooms. Cosmos makes a light, airy cut flower for summer bouquets.
Growing in pots
Compact varieties such as Sonata and the Cosmic series grow well in a pot at least 10 inches (25 cm) wide in full sun. Water when the mix dries and do not feed heavily.
Companion planting
Cosmos flowers feed pollinators and beneficial insects around summer vegetables.
Good companions
- Tomato Flowers at the bed edge bring in pollinators and predatory insects.
- Beans Shares the summer season and draws bees.
- Bell pepper A sunny summer neighbor that benefits from the visiting predators.
- Cucumber Cucumbers need bees to set fruit, and cosmos draws them.
- Marigold Another easy summer flower for a pollinator strip.
Pests and diseases
Cosmos needs only basic care; NC State lists a few common issues.
Pests to watch for
Diseases to watch for
- Powdery mildew White powdery coating on leaves, mostly late in summer.
- Aster yellows Yellowed, stunted growth and green, distorted flowers, spread by leafhoppers. Pull affected plants.
- Botrytis Gray mold on flowers and stems in wet weather.
Common questions
Why is my cosmos tall and floppy with few flowers?
Usually soil that is too rich, too much fertilizer or too much shade. Grow cosmos in lean soil in full sun and do not feed it.
When should I sow cosmos?
After the last frost once the soil is at least 65°F. In Florida and the Gulf South, sow in spring and again in late summer.
Does cosmos come back every year?
It is an annual, but it reseeds readily, so seedlings usually come up the following year.
How do I keep cosmos flowering?
Deadhead or cut flowers regularly. For Klondike cosmos covered in seed, cut the plants back to 12 to 18 inches and they will rebloom in about a month.
Is cosmos good for pollinators?
Yes. Its open, daisy-like flowers are visited by bees, butterflies and many beneficial insects, which makes it a good companion for vegetables.
Sources we checked: NC State Extension Gardener Plant Toolbox: Cosmos bipinnatus; NC State Extension Gardener Plant Toolbox: Cosmos sulphureus.
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